1. Field of the Invention
The present invention relates generally to an actuator arm assembly for a magnetic disk unit, and particularly to a structure of a spacer which is used for combining an actuator arm and a load beam.
2. Description of the Related Art
Recently, a magnetic disk unit, as a kind of an external storage device for a computer, is being made smaller and thinner. Also, reduced consumption of electric power is required. Moreover, improvement of the recording density of a magnetic disk (hard disk) is demanded in order to fulfil the requirement for larger capacity, and therefore, the number of hard disks loaded in the unit are increased.
In a typical magnetic disk unit for a computer, a constant start and stop (CSS) system is generally employed to regulate the relation between a magnetic head and a hard disk. In this system, during rotation of the magnetic disk, the magnetic head floats a very small distance above the disk due to the balance between a floating force caused by an air flow generated by the disk rotating at a high speed and a load beam for urging the magnetic head against the magnetic disk. When the rotation of the magnetic disk is stopped, the magnetic head is brought to a contactable area on the magnetic disk. Physical contact between the magnetic head and the magnetic disk is realized at this contactable area. During the time when the magnetic disk has stopped rotating, the head and the disk are held in contact with each other.
The magnetic head is supported on a distal end of a load beam, and a basal end portion of the load beam is secured to a distal end of an actuator arm through a spacer. That is, by spot welding the basal end portion of the load beam to the spacer and fixedly caulking the spacer to the distal end of the actuator arm, the load beam is firmly secured to the distal end of the actuator. As one method for caulking the spacer to the distal end of the actuator arm, a caulking ball is inserted into a round hole formed in the spacer in order to forcibly spread a cylindrical portion of the spacer, to thereby caulk the spacer into a hole formed in the actuator arm. Conventionally, for performing this caulking work, the spacer is pressed with a jig so that the surface of the spacer will not be deformed by a force acting on the spacer during the caulking work.
Since a recent magnetic disk unit is made smaller and thinner, the mounting distance of magnetic disks is also reduced. As a consequence, the thickness of the actuator and spacer is reduced, too. The reduced distance between adjacent magnetic disks gives rise to a problem in that a jig for pressing the spacer can not be inserted between adjacent actuator arms, and even if the jig can be somehow inserted therebetween, the pressing force is insufficient.
Also, if a load beam provided with a Cu pattern wiring to supply and receive a signal to and from the magnetic head is employed, it becomes difficult to press the load beam with the pressing jig during a caulking operation because of the provision of the pattern wiring on the load beam. Therefore, it gives rise to a problem that the spacer becomes warped during the caulking operation and the load beam, which is secured to the spacer, is deformed, thus adversely affecting the floating characteristic of the magnetic head.
Deformation of the space will be explained with reference to FIGS. 18A and 18B. As shown in FIG. 18A, a pair of spacers 3 are inserted into a circular hole la formed in a distal end portion of an actuator arm 1, one from the top and the other from the bottom. Then, a caulking ball 5 is inserted into holes 3a formed in the spacers 3 in a direction as shown by an arrow A, and the spacers 3 are fixedly caulked to the actuator arm 1. At that time, in the conventional structure, the spacers 3 are badly warped generally in proportion to a reduced thickness of the spacers 3 as shown in FIG. 18B. The warping of the spacers 3 is particularly significant at the time when no pressing jig is used, or when a pressing force of the jig is weak.